String readString;

Using Arduino Programming Questions
1

I have a sentence
String readString;
why readString is colored orange?

2

It just shows that readString is a 'Keyword'

Keywords are constants, variables, classes, methods, functions that the Arduino IDE knows about.

They are there to help you while you are coding.

They are also there to remind you not to use that word for your own function, class etc

so if you have

String readString;

in your code, it means that you're trying to declare readString as a String object.

readString is already defined, so you should probably use a different name for your String object

3

MovieFan1995:
I have a sentence
String readString;
why readString is colored orange?

Because readString() is a method in a class. Bad practice to use variable names or instance names that are method names or function names, even if you don't use the functions/methods.